1. Field of the Invention
The present invention generally relates to image forming apparatuses. More specifically, the present invention relates to an image forming apparatus including a carriage with a recording head configured to eject liquid drops.
2. Description of the Related Art
As an image forming apparatus such as a printer, facsimile machine, copier, plotter, or a multiple function processing machine including the printer, facsimile machine, copier, and the plotter, an inkjet recording apparatus is known. The inkjet recording apparatus is a liquid jet recording type image forming apparatus using a recording head configured to jet ink liquid drops.
In this liquid jet recording type image forming apparatus, the ink liquid drops are jetted from the recording head onto a conveyed sheet so that image forming such as recording or printing is performed. In the liquid jet recording type image forming apparatus, there are two kinds of image forming apparatuses. One is a serial type image forming apparatus configured to jet liquid drops so that an image is formed while a recording head moves in a main scanning direction. The other is a line type image forming apparatus using a line type head whereby liquid drops are jetted while the recording head does not move so that an image is formed.
Hereinafter, the “image forming apparatus” means an apparatus configured to jet liquid onto a medium such as a paper, thread, fiber, leather, hides, metal, plastic, glass, wood, or ceramic so that images are formed. The image forming apparatus includes a mere liquid jetting apparatus. In addition, “image forming” means not only providing an image of characters, figures, or the like on the medium but also providing an image such as a pattern having no meaning on the medium. “Image forming” includes adherence of the liquid drops onto the medium.
Furthermore, “ink” is not limited to the recording liquid or the ink and any liquid that is a fluid when being jetted can be applied as the liquid such as fixing liquid. In addition, “sheet” is not limited to a paper but includes an OHP sheet or leather. In other words, the sheet means a subject where the ink drop is adhered. The sheet includes a recorded medium, a recording medium, a recording paper, and a recording sheet.
In the serial type inkjet recording apparatus, a carriage having a recording head is slidably held by primary and secondary guide members. The carriage is moved in a main scanning direction by a main scanning moving mechanism such as a driving motor, a timing belt and a pulley.
In such an inkjet recording apparatus, it is necessary to keep a distance (gap) between the sheet and a nozzle surface of the recording head constant. If the gap is not constant, positional precision of adherence of the liquid drop onto the medium is degraded by, for example, reciprocating printing. In addition, since the thickness of the sheet is not always constant depending on kinds of the sheet, it is necessary to adjust the gap between the sheet and the nozzle surface of the recording head.
Because of this, a structure where a gap adjusting mechanism is provided has been known conventionally. As the gap adjusting mechanism, for example, i) a structure where a height position of the carriage is changed by elevating a frame and a guide member movably holding the carriage, ii) a structure where a height position of the carriage is changed by elevating a guide member of the carriage, iii) a structure where a conveyance belt configured to convey the sheet elevates, iv) a structure where a platen member facing the recording head and configured to guide the sheet elevates, or the like has been suggested.
In addition, the following structure has been also suggested. Plural shafts, a power transmitting member, and a rotating member are provided on a carriage. Each of the plural shafts has the same configuration where a part for providing a head holder holding the recording head is eccentric. The power transmitting member is provided between the plural shafts and configured to transmit a driving force. The driving part is configured to rotate the eccentric shaft. The plural shafts are arranged in parallel with each other. By rotating the rotating part, the plural shafts are rotated at the same angle so that the head holder goes upward and downward.
As shown in Japanese Laid-Open Patent Application Publication No. 2007-223232 and Japanese Laid-Open Patent Application Publication No. 2007-152792, a structure where the carriage is elevated for every main scanning guide member or the frame so that the gap between the recording head and the sheet conveyance surface is adjusted, is proper for a small sized inkjet recording apparatus.
However, in a recording apparatus for forming an image on a so-called large size and wide width medium, since the length in the main scanning direction is greater than 1000 mm and equal to or greater than 1500 mm, the weight of the entire carriage including the main scanning guide member or the frame and the carriage is equal to or greater than 10 kgf. Hence, it is difficult to elevate the carriage for every main scanning guide member or the frame with high precision.
The following structure has been suggested in Japanese Patent No. 3617626. The head holder configured to hold the recording head can be elevated relative to the carriage. The head holder hangs at the slider due to an energizing force of the spring. By using the cam mechanism, the head holder is elevated relative to the slider. With this structure, although the weight of a part which is elevated can be made light, if the number of the heads provided at the carriage is increased, the weight of the head holder is increased. Hence, it is difficult to stably hold the head.
The following structure has been suggested in Japanese Patent Application Publication No. 2005-271531. The holder configured to hold the head is provided in the carriage. The holder is provided on plural eccentric cams provided in parallel in the carriage. The eccentric cams are simultaneously rotated at the same angle so that the head with the holder is elevated. In this structure, if the number of the heads is increased, the weight of the head holder is increased. Hence, it is necessary to increase a diameter of the shaft of the eccentric cam. If the diameter of the shaft of the eccentric cam becomes larger, the width of the carriage becomes larger so that it is difficult to perform the driving control of the carriage. In addition, the width of the carriage becomes large so that the size of the apparatus becomes large.